The present invention relates to drive mechanisms which are particularly suitable for driving one or more displaceable elements which is or are guided to move along or around a predetermined path. Embodiments of the present invention are particularly suitable for driving machines such as braiding machines, knitting machines, circular weaving machines and the like, although many other applications for the invention are envisaged.
One problem which is frequently encountered in industry is that of driving a plurality of displaceable elements along or around a fixed path. The difficulty of driving such elements along or around the fixed path is mainly due to the problem of transmitting the drive to the elements. For example, in the case of braiding machines, it is required to move a number of carriages or spool carriers around a circular track. The carriages may occupy up to 75% of the track and it is essential that they are maintained at a regular spacing. In conventional machines drive is transmitted to the circulating carriages by various mechanical means, such as by cams engaging in cam tracks, by a plurality of gears spaced along the circular path, or by a plurality of picks, which are weighted levers spaced along the side of the path which the carriages are to follow, and which engage with a part of the carriages to move these a given distance along the track. Such known machines, however, are very noisy in operation, and they generate a considerable vibration, and out-of-balance forces causing wear of the rubbing parts, which limits the maximum speed at which they can be operated to a speed lower than that which is required for modern production.
The carriages circulating around the track of a braiding machine must be rotated at constant relative speeds so that their relative spacing is maintained. In one known type of machine there are two sets of carriages which are caused to move in a sinuous circular path representing that of the dancers around a maypole. In another known machine, the filaments which are to be interwoven with those carried by the carriages are carried on spools mounted on a disc which is rotated, with respect to the circulating carriages, in the opposite direction, the filaments from the disc mounted spools being guided over and under the filaments from the spools of the carriages by means of tube guides, known in the art as "wands". These wands lift the filaments to positions that clear the spools of the carriages as they pass, and then lower the filament between two adjacent carriages so that the next carriage passes over the filament guided by the wand.
Such braiding machines can be used for braiding any filamentary material and, as used in this Specification, the term "filament" will be understood to refer to any elongate thread, yarn or wire, whether nonfilament, multifilament, or fibrous form, which is suitable for braiding.
It is important for the proper operation of a braiding machine that the tension on the filaments should be maintained constant, as far as possible, and it should be possible to start up and slow down the machine while maintaining the relative spacings of the carriages on the track at all speeds.